Numerical investigations on pore-pressure response of suction anchors under cyclic tensile loadings

Abstract

The suction anchor is an effective option for the anchor foundations of floating offshore wind turbines (FOWTs). During its long-term service, in addition to the static pretension load, the suction anchor is subjected to a series of cyclic loads that are caused by waves, currents and the continuous motions of the floating structure. Thus, excess pore-pressure will accumulate within the soil around the embedded anchor, and the anchor capacity tends to be reduced. In this paper, by introducing the oscillatory and residual mechanisms, a novel numerical model is proposed to predict the instantaneous variations and accumulations of excess pore-pressures around a suction anchor that is subjected to long-term vertical cyclic loads. The results indicate that excess pore-pressure builds up mainly in the shallow soil near the external anchor wall. As a consequence, the effective soil stress in this region decreases along with the interface friction between the external wall and the soil. Detailed parametric studies reveal that the accumulation of excess pore-pressure is obvious for a larger load magnitude and smaller load period. With a lower permeability, smaller shear modulus or smaller relative density of the seabed soil, the pore-pressure accumulation outside the anchor increases significantly.